1. Field of Invention
The present invention is related to battery powered lanterns and lights and more specifically to an electronic control module for a lithium-ion battery powered lantern.
2. Background
It is the goal of every designer of battery-powered devices to prolong battery discharge life as much as possible. Battery life is particularly important in lanterns and other lighting devices used by firefighters and other emergency personal. Use of such battery powered lights in emergency environments is further complicated by the effect of increased or decreased temperatures in which the lights are used.
Li-ion batteries have a higher energy to weight ratio than any other commercially available rechargeable batteries. This makes them very desirable as a power source for portable devices. For safety, most Li-ion battery packs must have a safety circuit to protect them from over voltage, under voltage and over-discharge conditions. This presents some limitations for viable applications of Li-ion batteries. Namely, desired high discharge currents may not be possible because the battery protection circuit will not allow them. This controller safely allows high discharge currents from a Li-ion battery pack by controlling current to the main lamp. It prevents high currents from activating the safety circuit. It is possible to use a safety circuit that would allow higher currents, but this would also allow high currents during undesirable conditions such as a short circuit at the external charging contacts on the lantern. A high current short across these external contacts may result in an unsafe condition during use in hazardous locations.
At lower temperatures, the voltage is depressed. At higher temperatures the voltage is elevated.
Since low temperatures depress the voltage of Li-ion cells, application of a high power load further drops the cell voltage to the point that the protection circuit may activate and disconnect the load due to a low-voltage condition. This effect is further increased as the ratio of the size of the load to the capacity of the battery is increased.
In a typical lantern, main lamp is of the incandescent type, and can be of low power or high power. While a high power lamp produces more light, it draws much more current from the battery. As is well known, higher currents cause the battery to discharge rapidly and thus reduce the useful life of the battery charge. In addition to the nominal current drain resulting from the lamp in the “ON” condition, there is an initial spike of current that is many times the nominal. Further, because of the potential presence of in ignitable vapors, dust or other chemicals, the powering-up sequence of such lights must be carefully controlled as not to create a spark or other harmful electrical discharge. This “turn on” current spike can be large enough to cause a safety circuit, if present, to disconnect the battery from the load or appear as a short.
It is therefore a goal of manufacturers and users of battery powered lanterns to provide control over battery discharge that minimizes battery depletion and provides regulation of the start-up charge to maximize the safe operation of the lanterns in potentially hazardous environments. It is further goal to maximize battery depletion based on the temperature of the battery.